This invention relates generally to optical data storage and retrieval systems, and, more particularly, to such systems utilizing microfiche storage elements in the form of cards or sheets, each of which contains a number of separate frames or pages of optical information, greatly reduced in size from their original form. Thus, for example, many pages of a book or other document may be stored on a small fiche measuring only a few inches in each direction.
In a microfiche storage and retrieval system, means must be provided for storing a large number of such fiche elements, and for retrieving any selected frame of information on command. One convenient way to accomplish this is to place the fiche in generally radial positions in a circular carousel. When a selection command is provided to the system, typically through a keyboard, the carousel is rotated with respect to a stationary retrieval station until a desired fiche is positioned in an operative relationship with the station, then the fiche is withdrawn and conveyed to an x-y positioning mechanism, which translates the selected fiche in two dimensions to locate the selected frame or page. An optical viewing system then displays the selected page on a screen. When another command is given, the selected fiche is replaced in its original position in the carousel, after which the carousel may be rotated again to locate the next desired frame of information. Such a system is fully described in U.S. Pat. No. 3,429,436 issued in the name of Eugene H. Irasek.
The principal limitation of the carousel microfiche systems of the general type described above is one of storage capacity. A number of microfiche applications, including, for example, searching some of the larger subclasses in the Patent and Trademark Office patent files, require a much larger microfiche capacity than is available from a single carousel. Although a number of retrieval devices may be interconnected and controlled by means of a computer, such an arrangement is cumbersome in some respects, and uses storage space inefficiently. Moreover, the computer is a costly component of the system, and may not be needed for purposes other than controlling multiple carousels.
Accordingly, there is a definite need in this field for a carousel-type microfiche storage and retrieval system with a capacity much larger than is presently available in single-carousel systems. The present invention satisfies this need.